Moving armature receivers are widely used to convert electrical audio signals into sound in portable communication applications such as hearing instruments, headsets, in-ear-monitors, earphones etc. Moving armature receivers convert the electrical audio signal to sound pressure or acoustic energy through a motor assembly having a movable armature. The armature typically has a displaceable leg or segment that is free to move while another portion is fixed to a housing or magnet support of the moving armature receiver. The motor assembly includes a drive coil and one or more permanent magnets, both capable of magnetically interacting with the armature. The movable armature is typically connected to a diaphragm through a drive rod or pin placed at a deflectable end of the armature. The drive coil is electrically connected to a pair of externally accessible drive terminals positioned on a housing of the miniature moving armature receiver. When the electrical audio or drive signal is applied to the drive coil the armature is magnetized in accordance with the audio signal. Interaction of the magnetized armature and a magnetic field created by the permanent magnets causes the displaceable leg of the armature to vibrate. This vibration is converted into corresponding vibration of the diaphragm due to the coupling between the deflectable leg of the armature and the diaphragm so as to produce the sound pressure. The generated sound pressure is typically transmitted to the surrounding environment through an appropriately shaped and sized sound port or spout attached to the housing or casing of the moving armature receiver.
However, the vibration of the deflectable leg of the armature and corresponding vibration of the diaphragm causes a housing structure of the moving armature receiver to vibrate in a complex manner with vibration components generally extending in all spatial dimensions e.g. along a longitudinal housing plane (e.g. chosen as x-axis direction) and housing planes perpendicular thereto (e.g. chosen as y-axis and z-axis directions).
These vibration components are undesirable in numerous applications such as hearing instruments or other personal communication devices where these vibrations may cause feedback oscillation due to the coupling of mechanical vibration from the housing of the moving armature receiver to a vibration sensitive microphone of the personal communication device. Moving armature receivers or loudspeakers have therefore conventionally been mounted in resilient suspensions in many types of personal communication device such as Behind-The-Ear and In-The-Ear hearing aids to suppress or attenuate mechanical vibrations to prevent these from being transmitted to a microphone of the hearing aid. Conventional or prior art resilient suspensions include elastomeric rubber boots and elastomeric strips or ribbons mounted to partly or fully enclose the receiver housing. However, these resilient suspensions exhibit relatively small compliance or large stiffness along a longitudinal housing plane of the receiver while exhibiting a much larger compliance in the housing planes transversal to the longitudinal housing plane.
In prior art moving armature receivers efforts have been made to reduce the level of vibration for example by designing dual-diaphragm receivers such that a first and a second armature have been arranged in a mirror-symmetrical fashion about a central longitudinal housing plane extending through the dual-diaphragm receiver. U.S. Pat. No. 4,109,116 discloses such a miniature dual-diaphragm moving armature receiver for hearing aid applications. The dual-diaphragm receiver is formed as a back-to-back mounted assembly of two conventional single diaphragm moving armature receivers to achieve suppression of mechanical vibrations of the receiver. The disclosed dual-diaphragm receiver comprises a pair of U-shaped armatures mounted mirror-symmetrically around a central longitudinal plane extending in-between a pair of abutted separate housing structures. During operation, deflectable legs of the two U-shaped armatures, and respective diaphragms coupled thereto, move in opposite directions in a plane perpendicular to the central longitudinal housing plane to suppress vibrations along the perpendicular plane.
Unfortunately, this type of mirror-symmetrical dual-receiver design is not very efficient in cancelling or attenuating mechanical vibrations along the central longitudinal plane of the receiver housing. The linkage segments of the U-shaped armatures will move simultaneously in the same longitudinal direction so as to reinforce vibration instead of cancelling vibration in the longitudinal plane.
Since the U-shaped armature geometry generally possesses numerous advantageous properties such as large armature compliance for given armature dimensions and a small width, a moving armature receiver assembly based on two or more U-shaped armatures with a reduced level of housing vibration, in particular along the longitudinal housing plane of the receiver, would be an improvement in the art.